This invention relates to stable, built, enzyme-containing liquid detergent compositions suitable for laundry or pre-soak formulations. More particularly, the invention relates to aqueous enzyme-containing liquid detergent compositions which contain one or more detergent builders and which are characterized by being physically stable, homogeneous liquid compositions, having improved enzyme stability. The invention also relates to the novel stabilized enzyme preparation useful as a laundry additive, as well as to the novel enzyme stabilization system, per se.
The formulation of stabilized enzyme-containing liquid detergent compositions has been the focus of much attention in the prior art. The desirability of incorporating enzymes into detergent compositions is primarily due to the effectiveness of proteolytic and amylolytic enzymes in decomposing proteinaceous and starch materials found on soiled fabrics, thereby facilitating the removal of stains, such as, gravy stains, blood stains, chocolate stains and the like during laundering. However, enzymatic materials suitable for laundry compositions, particularly proteolytic enzymes, are relatively expensive. Indeed, they generally are among the most expensive ingredients in a typical commercial liquid detergent composition, even though they are present in relatively minor amounts. Moreover, enzymes are known to be unstable in aqueous compositions. It is for this reason that an excess of enzymes is generally required in liquid detergent formulations to compensate for the expected loss of enzyme activity during prolonged periods of storage. Accordingly, the prior art is replete with suggestions for stabilizing enzyme-containing liquid detergent compositions, and in particular by the use of various materials which are incorporated into the composition to function as enzyme stabilizers.
In the case of liquid detergent compositions containing a builder, the problem of enzyme instability is particularly acute. Primarily this is because detergent builders have a destabilizing effect on enzymes, even in compositions containing enzyme stabilizers which are otherwise effective in unbuilt formulations. Moreover, the incorporation of a builder into a liquid detergent composition poses an additional problem, namely, the ability to form a stable single-phase composition; the solubility of sodium tripolyphosphate, for example, being relatively limited in aqueous compositions, and especially in the presence of anionic and nonionic detergents.
Attempts to stabilize enzyme activity in aqueous media are extensively described in the patent literature. Among the approaches to the problem of enzyme stabilization has been the use of various organic materials, such as alcohols, polyols, acids, esters and sugars which are said to have a stabilizing effect upon enzymes. Water-soluble calcium salts and boron compounds have also been used to stabilize enzyme compositions. Thus, for example, U.S. Pat. No. 4,253,543 to Guilbert seeks to provide enzyme stability by adding an anti-oxidant and a polyol to aqueous detergent compositions. U.S. Pat. No. 4,111,855 ,to Barrat, et al. uses a combination of from about 0.05 to about 1.5% by weight of a polyacid capable of forming water-soluble Cacomplexes, such as citric acid, and calcium ion in an amount of from 0.5 to 15 millimoles per liter as an enzyme stabilizer.
U.S. Pat. No. 4,287,082 to Tolfo, et al. discloses homogeneous enzyme-containing liquid detergents characterized by the presence of a C.sub.10 -C.sub.16 saturated fatty acid, calcium ion and a C.sub.1 -C.sub.3 short chain monocarboxylic acid or salt thereof.
U.S. Pat. No. 4,318,818 to Letton, et al. also describes an enzyme composition which is stabilized by calcium ion and a short chain length carboxylic acid salt. A polyacid may also be present in the compositions of Letton, et al. as well as those of Tolfo, et al.
In U.K. Patent Application G.B. 2,079,305, published Jan. 20, 1982 and Canadian Patent 1,092,036, there is disclosed an aqueous built enzyme-containing liquid detergent composition which is stabilized by a mixture of a polyol and boric acid.
In U.S. Pat. No. 4,532,064, there is disclosed an aqueous enzyme-containing liquid detergent composition containing an enzyme stabilizing mixture consisting of certain dicarboxylic acids and borax. The dicarboxylic acids of the formula COOH--(CHOH).sub.a --(CH.sub.2).sub.b --(CHOH).sub.c --(CH.sub.2).sub.d --COOH in which a, b, c, d are whole numbers from 0 to 4, the sum a+b+c+d=0 to 4, or the alkali metal, ammonium, alkanolamine or alkaline earth metal salts thereof, are recommended as a substitute for a polyol such as glycerol in known enzyme stabilizing mixtures consisting of glycerol and a boron compound. However, such dicarboxylic acidborax mixtures in common with the aforementioned mixtures of glycerine and borax provide only a modest stabilizing effect in unbuilt liquid detergent compositions, especially under freezethaw conditions.
U.S. Pat. No. 4,529,525 to Dormal, et al. discloses an unbuilt stabilized enzyme-containing liquid detergent composition comprising: (a) from about 5 to about 75%, by weight, of one or more non-soap detergent surface active agents selected from the group consisting of anionic, nonionic, cationic, ampholytic and zwitterionic detergent compounds; (b) from about 0.1 to about 20 millimoles of calcium ion per liter of composition; (c) from about 0.05 to about 5%, by weight, of an enzyme selected from the group consisting of proteases, amylases and mixtures thereof; (d) from about 0.1 to about 10%, by weight, of a stabilizing agent comprising (i) at least one water-soluble salt of a dicarboxylic acid represented by the formula (CH.sub.2)n(COOH).sub.2 wherein n is an integer from 1 to 6; and/or (ii) at least one water-soluble salt of an unsaturated dicarboxylic acid selected from the group consisting of fumaric acid and maleic acid; (e) from about 0 to about 25%, by weight, of a soap comprising a water-soluble salt of a saturated fatty acid having 10 to 18 carbon atoms in the alkyl chain; and (f) the balance water and optionally a sequestrant. This patent also illustrates two formulations containing sodium borate in place of a dicarboxylic acid of the above formula. Sodium tartrate is also exemplified in specific formulations.
U.S. Pat. No. 4,842,769 to Shulman, et al. discloses a stabilized fabric softening built, enzyme-containing liquid detergent composition comprising:
(a) from about 5 to 20%, by weight, of one or more surface active detergent compounds selected from the group consisting of anionic, nonionic and amphoteric detergent compounds;
(b) from about 5 to 30%, by weight, or one or more builder salts selected from the group consisting of alkali metal tripolyphosphates, alkali metal carbonates, alkali metal nitrilotriacetates, and polyacetal carboxylates;
(c) from about 5 to 20%, by weight, of a swelling bentonite clay;
(d) an effective amount of an enzyme or an enzyme mixture selected from the group consisting of alkaline protease enzymes and alpha-amylase enzymes;
(e) an enzyme-stabilizing system containing, based on the weight of the detergent composition, (i) from about 1 to 10% glycerine; (ii) from about 1 to 8% of a boron compound selected from the group consisting of boric acid, boric oxide, and alkali metal borates and, (iii) from about 0.5 to 8% of a carboxylic acid compound selected from the group consisting of mono, di and/or polycarboxylic acids having 1 to 8 carbon atoms, and which may contain hydroxy or amino substituents, and water-soluble salts thereof; and
(f) the balance comprising water and optionally perfume and other adjuvants.
The related U.S. Pat. Nos. 4,537,706 and 4,537,707 to Severson, Jr. each disclose heavy-duty liquid detergent compositions comprising, by weight:
(a) from about 10% to about 50% of an anionic synthetic surfactant;
(b) from about 3% to about 30% of a C.sub.10 -C.sub.22 fatty acid;
(c) from about 2% to about 15% of a water-soluble detergency builder;
(d) from about 0.01% to about 5% of a proteolytic or amylolytic enzyme;
(e) from about 0.25% to about 10% of boric acid or a boron compound capable of forming boric acid in the composition;
(f) from about 1 to about 30 millimoles of calcium ion per liter of composition; and
(g) from about 20% to about 80% of water; and in the '707 patented composition
(h) from about 0.05% to about 5% of a water-soluble formate. The compositions may also include various optional ingredients, including the known polyol enzyme stabilizers. The polycarboxylates are disclosed as preferred builders and citrates as highly preferred builder materials. The formulations of Example I of these patents include a polyacid, i.e. citric acid (anhydrous) in an amount of 4.0 weight%. The exemplified levels of boric acid range from 0.5 to 2.0% and the exemplified calcium ion concentrations range from 9.65 to 15.6 millimoles per liter.
In our commonly assigned copending application Ser. No. 07/255,817 filed Oct. 7, 1988, titled HEAVY DUTY FABRIC SOFTENING LAUNDRY DETERGENT COMPOSITION, the disclosure of which is incorporated herein in its entirety by reference, a highly advantageous "softergent" liquid composition based on a combination of anionic and nonionic surfactants and a certain type of amphoteric surfactant, inorganic builder, bentonite and water is disclosed. These compositions may, and preferably do, also include enzyme(s) and enzyme stabilization system. The enzyme stabilizer system includes 0.5 to 5% of a mixture of dibasic acid of 4 to 6 carbon atoms each, 1 to 3% of boric acid and 0.1 to 0.5% of a source of calcium ion. However, as will be shown in the examples which follow, the stabilizing power of this stabilization system is less efficient than the stabilization system according to this invention.
While many of these previously described formulations have been able to extend the useful life of the enzyme component(s) under normal or slightly elevated temperatures, e.g. 90.degree. F., 100.degree. F. or 110.degree. F (in Canadian Patent 1,092,036 enzyme stabilization was measured at about 133.degree. F. to 140.degree. F.), still further improvements are desired, especially with regard to the enzyme stabilization for enzyme containing compositions subjected to more severe storage conditions, such as freeze-thaw conditions.